In one aspect, the invention relates to an apparatus for conducting a pultrusion process. In another aspect, the invention relates to a pultrusion process. In a still further aspect, the invention relates to a product resulting from a pultrusion process.
The production of pultruded products from thermoset resin such as polyester resin is well known. In this process, a glass fiber roving is pulled from a creel, passed through a liquid polyester resin bath for impregnation of the roving with the resin and subjected to final shaping and curing in a heated die. A puller is located in the process after the curing die for causing the roving to be forwarded through the processing system. The roving can be formed from other types of fibers such as carbon fiber or aramid fiber and other liquid thermoset resin such as vinyl ester resin or epoxy resin can be used as the matrix material if desired.
Pultrusion processes employing thermoplastic resins for the matrix material are not nearly so well known. Where a liquid bath of molten thermoplastic resin is used, the high viscosity of the molten resin and poor wetout of the roving causes processing problems. Also, many thermoplastic resins will degrade when held in the molten state, usually by undergoing crosslinking reactions, becoming of even higher molecular weight and higher viscosity. It is thus difficult to provide a uniform product from a pultrusion process employing a molten bath of liquid thermoplastic resin. A pultrusion process capable of providing a uniform thermoplastic product would be very desirable.
Pultruded articles are generally characterized by parallel fibers aligned parallel to the longitudinal axis of the article. Such articles are highly anisotropic where all of the reinforcing fibers are parallel to the article's longitudinal axis. For many applications, pultruded articles are not entirely suitable because of inadequate isotropic properties. A pultrusion device and process for providing a pultruded product having greater isotropic properties would thus be very desirable.
For many applications, a high degree of surface smoothness in the pultruded product is required. Also, because of the tendency of the reinforcing fibers to wick liquids into the article weakening it, providing a smooth and/or resin enriched surface to seal off the fibers could be desirable for certain applications.
When utilizing slurry impregnation of filament rovings with thermoplastic particles it is increasingly difficult to obtain good fiber wet out and low void content as the pultruded article becomes increasingly larger in cross section. A process for making large pultruded articles such as rods, bars and I-beams from slurry impregnated rovings with the resulting article having good fiber wet out and low voids would be very desirable.